add build instructions

README.md

@@ -24,3 +24,20 @@ the following are currently supported:
 - [md4c](https://github.com/mity/md4c) for markdown parsing
 - [ansi-term](https://github.com/ziglibs/ansi-term) wraps ansi styling
 - [zig-clap](https://github.com/Hejsil/zig-clap) for arg parsing
+
+## building
+1. install [zig 0.13.0](https://ziglang.org/download/#release-0.13.0)
+2. clone repo
+3. run `zig build`
+
+if you want a release build:
+
+4. run `zig build --release=small`
+
+release optimize modes are:
+
+- fast
+- safe
+- small
+
+the mdcat binary will be in `zig-out/bin/mdcat`